Framing for an adaptive modulation communication system

ABSTRACT

A system and method for mapping a combined frequency division duplexing (FDD) Time Division Multiplexing (TDM)/Time Division Multiple Access (TDMA) downlink subframe for use with half-duplex and full-duplex terminals in a communication system. Embodiments of the downlink subframe vary Forward Error Correction (FEC) types for a given modulation scheme as well as support the implementation of a smart antennae at a base station in the communication system. Embodiments of the system are also used in a TDD communication system to support the implementation of smart antennae. A scheduling algorithm allows TDM and TDMA portions of a downlink to efficiently co-exist in the same downlink subframe and simultaneously support full and half-duplex terminals. The algorithm further allows the TDM of multiple terminals in a TDMA burst to minimize the number of map entries in a downlink map. The algorithm limits the number of downlink map entries to not exceed 2n+1, where n is the number of DL PHY modes (modulation/FEC combinations) employed by the communication system.

RELATED APPLICATIONS

This application claims priority to a U.S. provisional patentapplication Ser. No. 60/249,065, filed Nov. 15, 2000, titled “FramingFor an Adaptive Modulation Communication System,” which is herebyincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to frame structures for communication systems andmore particularly to frame structures for adaptive modulation wirelesscommunication systems.

2. Description of Related Art

A wireless communication system facilitates two-way communicationbetween a plurality of subscriber units (fixed and portable) and a fixednetwork infrastructure. Exemplary communication systems include mobilecellular telephone systems, personal communication systems (PCS), andcordless telephones. The key objective of these wireless communicationsystems is to provide communication channels on demand between theplurality of consumer subscriber units and their respective basestations in order to connect the subscriber unit user with the fixednetwork infrastructure.

Subscriber units typically communicate through a terminal with the basestation using a “duplexing” scheme thus allowing the exchange ofinformation in both directions of connection. Transmissions from thebase station to the terminals are commonly referred to as “downlink”transmissions. Transmissions from the terminals to the base station arecommonly referred to as “uplink” transmissions. In wireless systemshaving multiple access schemes a time “frame” is used as the basicinformation transmission unit.

Depending upon the design criteria of a given system, systems havetypically used either time division duplexing (TDD) or frequencydivision duplexing (FDD) methods to facilitate the exchange ofinformation between the base station and the terminals. In a TDDcommunication system, the base station and the terminals use the samechannel, however, their downlink and uplink transmissions alternate oneafter the other to prevent interference. In a FDD communication system,the base station and the terminals use different channels for theirdownlink and uplink transmissions, respectively. Thus, the concern forinterference between uplink and downlink transmissions is mitigated in aFDD communication system as compared to a system using TDD. However, theincreased cost and complexity in deploying a FDD communication systemoften outweighs this obvious advantage over a TDD communication system.

In both TDD and FDD systems, each base station and terminal includes amodem configured to modulate an outgoing signal and demodulate anincoming signal. If the modem is configured to modulate and demodulatesimultaneously, the modem is a “full-duplex” modem. If the modem is notconfigured to modulate and demodulate simultaneously, but ratherswitches between modulating and demodulating, the modem is a“half-duplex” modem.

In an exemplary FDD communication system, each terminal's modem operatessimultaneously to transmit and receive information in a full-duplexmanner. Such a terminal can continually receive data from the basestation. By continually receiving information, the terminal is able tomaintain its synchronization with the base station. By maintaining itssynchronization, the terminal is less dependent on the base stationtransmitting control information and preambles to assist the terminal inlocating its data within the downlink.

Because a half-duplex terminal does not receive information from thebase station when the terminal transmits it uplink to the base station,it may fall out of synchronization with the base station. When thisoccurs, the terminal may require the base station to downlink additionalcontrol information or a preamble to allow the terminal tore-synchronize prior to it receiving downlink data from the basestation.

SUMMARY OF THE INVENTION

The systems and methods have several features, no single one of which issolely responsible for its desirable attributes. Without limiting thescope as expressed by the claims which follow, its more prominentfeatures will now be discussed briefly. After considering thisdiscussion, and particularly after reading the section entitled“Detailed Description” one will understand how the features of thesystem and methods provide several advantages over traditional framingtechniques.

One aspect is a frequency division duplexing (FDD) wirelesscommunication method for use by a base station, at least one full-duplexterminal, and at least one half-duplex terminal, wherein the basestation transmits using a downlink subframe on a first channel and thefull-duplex and half-duplex terminals transmit using an uplink subframeon a second channel, wherein the downlink subframe includes a broadcastpreamble, a time division multiplex (TDM) portion, and a Time DivisionMultiple Access (TDMA) portion, and wherein the TDMA portion includes atleast one modulation/forward error correction (PHY) mode with anassociated preamble, both of which are intended for the at least onehalf-duplex terminal. The method comprises transmitting a broadcastpreamble from a base station to a full-duplex terminal and a half-duplexterminal during a downlink subframe on a first channel, synchronizingthe full-duplex terminal and the half-duplex terminal to the basestation based on the broadcast preamble, transmitting modulated datafrom the half-duplex terminal to the base station during an uplinksubframe on a second channel, and transmitting modulated data from thebase station to the full-duplex terminal during a TDM portion of thedownlink subframe on the first channel after the full-duplex terminal issynchronized with the base station. The method further includestransmitting a preamble by the base station during a TDMA portion of thedownlink subframe on the first channel, wherein the preamble istransmitted after the half-duplex terminal has transmitted its modulateddata to the base station, re-synchronizing the half-duplex terminal withthe base station based on the preamble transmitted by the base stationon the first channel.

Another aspect is a system for a frequency division duplexing (FDD)wireless communication system including a base station, at least onefull-duplex terminal, and at least one half-duplex terminal, wherein thebase station transmits using a downlink subframe on a first channel andthe full-duplex and half-duplex terminals transmit using an uplinksubframe on a second channel, wherein the downlink subframe includes abroadcast preamble, a time division multiplex (TDM) portion, and a TimeDivision Multiple Access (TDMA) portion, and wherein the TDMA portionincludes at least one modulation/forward error correction (PHY) modewith an associated preamble, both of which are intended for the at leastone half-duplex terminal. The system comprises at least one half-duplexterminal configured to alternate between transmitting on a first channeland receiving on a second channel, at least one full-duplex terminalconfigured to transmit on the first channel while receiving on thesecond channel, and a base station configured to transmit a broadcastpreamble to the half-duplex terminal and the full-duplex terminal duringa TDM portion of a downlink subframe and to transmit a preamble during aTDMA portion of the downlink subframe, wherein the half-duplex terminalsynchronizes with the base station based on the broadcast preamble andre-synchronizes with the base station based on the preamble.

Still another aspect is a method for scheduling modulation/forward errorcorrection (PHY) modes for a frequency division duplex (FDD)communication system which includes a plurality of terminals and a basestation, both configured to communicate using adaptive modulations in adownlink subframe and an uplink subframe, with each of the plurality ofterminals having an associated preferred downlink PHY mode, D1, D21, . .. DN, wherein D1 is a most robust modulation and DN is a least robustmodulation, and wherein each of the plurality of terminals and theirassociated preferred downlink PHY mode have an associated uplink PHYmode, U1, U2, UN, and wherein U1 is associated with the plurality ofterminals that have the preferred downlink PHY mode D1, and wherein UNis associated with the plurality of terminals that have the preferreddownlink PHY mode DN, such that a number of downlink map entries doesnot exceed 2N+1. The method comprises grouping the plurality ofterminals based on preferred downlink PHY modes, allocating uplinkbandwidth in an uplink subframe such that the plurality of terminals areput in order of their preferred downlink PHY modes, from a second mostrobust preferred downlink PHY mode and continuing in order of decreasingrobustness with a most robust preferred downlink PHY mode last,allocating the plurality of terminals that use a D1 PHY mode to begin ata start of a downlink subframe, and if a time duration for the pluralityof terminals that have a DN PHY mode is less than a time duration forthe plurality of terminals that are assigned to a UN+1 PHY mode,allocating bandwidth of the downlink subframe to the plurality ofterminals that use the DN PHY mode, beginning at a time that a UN PHYmode ends. The method further includes that if the time duration for theplurality of terminals that have the DN PHY mode is greater than orequal to the time duration for the plurality of terminals that areassigned to the UN+1 PHY mode, allocating bandwidth of the downlinksubframe to the plurality of terminals that use the DN PHY mode,beginning at an end of a DN−1 PHY mode, if the time duration of theplurality of terminals that have the DN PHY mode is longer in durationthan a combined time duration of a U1 PHY mode and gaps that are notaligned with the UN PHY mode, rearranging downlink bandwidth of thedownlink subframe to accommodate a remainder of the DN PHY mode suchthat the remainder is not aligned with the UN PHY mode, and if the timeduration of the plurality of terminals that have the DN PHY mode isshorter in duration than the combined time duration of the U1 PHY modeand the gaps that are not aligned with the UN PHY mode, allocatingbandwidth of the downlink subframe to the plurality of terminals thatuse the DN PHY mode, beginning at the end of the DN−1 PHY mode and alsointerleaved in the gaps in the downlink subframe.

Still other aspects include methods and systems for use in a TDDcommunication system to support the implementation of smart antennae.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a configuration of a communication system with abase station and several associated terminals.

FIG. 2 is a diagram of an exemplary time division duplex (“TDD”) framestructure along with an exemplary mapping structure.

FIG. 3 is a block diagram of an exemplary transmitter.

FIG. 4 is a block diagram of an exemplary receiver.

FIG. 5 is the TDD frame structure from FIG. 2 adapted for FDD operation.

FIG. 6 shows an arrangement for user data from multiple terminals in aTDM time block.

FIG. 7 shows a downlink conflict for a FDD unit restricted to halfduplex operation.

FIG. 8 is a mapping diagram for a combined FDD TDM/TDMA downlinksubframe.

FIG. 9 shows an exemplary downlink map structure.

FIG. 10 shows an exemplary relationship between frame mapping data andthe data it maps for a FDD communication system.

FIG. 11 is a mapping diagram for an FDD TDM/TDMA downlink subframe whichvaries PHY modes based on modulation and FEC.

FIG. 12 is a mapping diagram for a TDD TDM/TDMA downlink subframe thatsupports smart antennae.

FIG. 13 is a flow chart for a scheduling algorithm.

FIG. 14 shows an ordering of uplink PHY modes, U₂, U₃, U₄, U₅, U₁,within an uplink subframe.

FIG. 15 represents the situation where the duration of downlink PHY modeD1 equals or exceeds the duration of uplink PHY mode U₂.

FIG. 16 represents the converse case to FIG. 15, in which the durationof downlink PHY mode D₁ is less than the duration of uplink PHY mode U₂.

FIG. 17 represents the situation where the duration of uplink PHY modeU₃ exceeds the duration of downlink PHY mode D₂.

FIG. 18 represents the situation where the duration of downlink PHY modeD₃ exceeds the combined duration of uplink PHY modes U₄, U₅, and U₁.

FIG. 19 represents the situation where the duration of downlink PHY modeD₃ is less than the duration of uplink PHY mode U₄.

FIG. 20 represent the situation where the duration of downlink PHY modeD₄ is less than the duration of uplink PHY mode U₅.

FIG. 21 represents a scheduling of downlink PHY mode D₅ within thedownlink subframe that results in PHY mode D₅ having to transmit whileit receives.

FIG. 22 represents further rearrangement of downlink PHY mode D₅ withdownlink PHY mode D₃ so that downlink PHY mode D₅ does not transmitwhile it receives.

DETAILED DESCRIPTION

The following detailed description is directed to certain specificembodiments of the invention. However, the invention can be embodied ina multitude of different systems and methods. In this description,reference is made to the drawings wherein like parts are designated withlike numerals throughout.

FIG. 1 is a diagram of an exemplary cell 10 that includes a base station20 located centrally in cell 10 and a plurality of terminals 30, 32, 34,36, 38 associated with the base station. FIG. 1 does not show buildingsor other physical obstructions (such as trees or hills, for example),that may cause channel interference between signals of the terminals.The terminals and the base station communicate by transmitting radiofrequency signals. The term channel is used to mean a band or range ofradio frequencies of sufficient width for communication, e.g., 25.500GHz to 26.525 GHz (a 25 MHz wide channel). Although the followingdiscussion relates to a system that transmits information within theLocal Multi-Point Distribution Services (LMDS) band at frequencies ofapproximately 28 GHz, the system is not so limited. Embodiments of thesystem are designed to transmit information between the terminals andbase station at frequencies, for example, of 10 GHz to 66 GHz usingQuadrature Amplitude Modulation (QAM) symbols. The base station andterminals use adaptive modulation and forward error correction (FEC)schemes to communicate. Adaptive modulation, or adaptable modulationdensity, includes varying the bit per symbol rate modulation scheme, ormodulation robustness, of signals transmitted between a terminal and abase station. Adaptive FEC includes varying the amount of errorcorrection data that is transmitted in the signal. Both the modulationand FEC can be adapted independently to transmit data between the basestation and terminals. For ease of explanation, the phrase “PHY mode” isused to indicate a combination of a selected modulation scheme with aselected FEC.

The systems and methods described herein can also be implemented in aMultichannel Multi-point Distribution Service (MMDS) which operatesbelow 10 GHz. In the MMDS, Orthogonal Frequency Division Multiplexing(OFDM) symbols may be transmitted between the base station and terminalsas an alternative to QAM modulation. In such a system, the methods andsystems are applied to one or more of the OFDM subchannels.

The PHY mode(s) selected for use in the cell 10 is normally determinedas a function of the geographical relationship between the BS and theterminal, the rain region, and the implementation or modem complexity ofthe terminals. However, the selection of a single PHY mode based on thelowest bit per symbol rate modulation scheme and maximum FEC supportedby all terminals may not optimize bandwidth utilization within the cell10. In particular, better environmental conditions, e.g., less distance,between some terminals (such as units 38, 30 for example) and the BS maypermit the use of a less robust PHY mode that has an error level belowthe maximum desirable error level.

FIG. 2 is diagram of an exemplary physical layer frame structure for usein the cell 10 that enables adaptive PHY modes to be employed. FIG. 2also illustrates a process for mapping data to the physical layer framestructure for transmission to one or more terminals. The PHY mode may bemodified from frame to frame or remain constant for a plurality offrames for a particular terminal. Further, a terminal may select orindicate a preferred PHY mode.

Frame 80 includes a plurality of time blocks. The total time duration ofthe plurality of time blocks in frame 80 can vary. For example, timedurations of 0.5 msec, 1 msec, and 2 msec could be used. In this examplethere are ten time blocks where the first through fifth time blocks arefor a downlink subframe 83. The downlink subframe contains downlink data82(a)–82(n) (from the base station 10 to one or more terminals). Thesixth through tenth time blocks form an uplink subframe 85. The uplinksubframe contains uplink data 84(a)–84(n) (to the base station 10 fromone or more terminals). Data within a single time block is transmittedor received using a single PHY mode.

In this example, each downlink subframe time block has a different PHYmode, e.g. DM₁, DM_(2, DM) _(3, and DM) ₄. The data transmitted usingeach downlink PHY mode is intended for one or more terminals. Thereceiving terminal will retrieve data that was transmitted using itspreferred PHY mode and/or a more robust PHY mode. Many terminals may beassigned to any one downlink PHY mode where each terminal retrieves itsdata during the same time block based on an address or identifier.Consequently, a terminal may only retrieve data from a portion of a timeblock.

Still referring to FIG. 2, the uplink subframe time blocks areassociated with PHY modes, e.g. UM₁, UM₂, UM₃, and UM₄. Uplink timeblocks are assigned to terminals for transmission of data from one ormore terminals to the base station. Multiple terminals may be assignedto a single time block based on the terminals preferred PHY mode. Forexample, terminals 30, 38 could be assigned to UM₁. The length of theUM₁ will account for the bandwidth requirements of both terminals. Insuch a case, a transition gap (not shown) may be included between theportions of the uplink subframe time block, UM₁, that are assigned tothe two terminals. The transition gap can include a preamble for thebase station to synchronize with the transmitting terminal. As with thedownlink PHY modes, an individual terminal may be assigned more than oneuplink PHY mode.

The length, or duration, of each time block can vary. The PHY modes usedfor the data in each time block can also vary for each downlink anduplink time block between frames. Varying the time duration of theuplink and downlink time blocks, PHY modes, is generally useful, sinceuplink and downlink data amounts are likely to vary. The TDD framestructure may apply adaptive PHY modes only for the downlink and use adifferent scheme for the uplink. For example, a fixed modulation schemecould be used for the uplink. Conversely, a different scheme (e.g. fixedmodulation) can be used on the downlink, while using adaptive PHY modeson the uplink.

A scheduling approach is used to arrange data from terminals within theframe 80. An uplink scheduling approach may be selected independentlyfrom the downlink scheduling approach. The uplink/downlink schedulingapproaches may be based on physical layer issues, including interferenceminimization, propagation delays (including round trip delays), etc., aswell as modulation use (specific ordering by PHY mode). Alternatively,the uplink/downlink scheduling approaches may be based completely ondata traffic requirements and not on physical layer issues.

One downlink scheduling approach arranges the PHY modes such that DM₁(most robust)≦DM₂≦DM₃≦DM₄ (least robust). Thus, the data in the downlinksubframe is arranged from the most robust PHY mode to the least robustPHY mode. Each terminal listens to its preferred PHY mode and any PHYmodes that are more robust than its preferred PHY mode. The terminalsreceive all of the data they are capable of receiving, and can keep ordiscard portions of the data depending on whether the data is intendedfor them. By using this scheduling approach, each terminal is able tomaintain its synchronization with the base station from the start of thedownlink subframe, through PHY modes that are more robust than itspreferred PHY mode, and finally during its preferred PHY mode.

The uplink scheduling information may be conveyed to the terminals by amap through control data 86. The control data 86 may be located at thestart of the downlink subframe 83. The control data 86 can indicatewhere the PHY mode transitions occur within the frame 80. A typical mapis a list of time indicators pointing out transmission location (such asby referencing start and end, or start and length, or offsets relativeto a previous transmission). The map can also include terminalidentification associating the map entry with a specific terminal. Thecontrol data 86 can be encoded using the most robust PHY mode of thesystem. An exemplary downlink map is discussed below with reference toFIG. 9.

Still referring to FIG. 2, an unsolicited region 88 of the uplinksubframe 85 is used by the terminals to communicate control information,such as, bandwidth and registration requests, to the base station.Information placed in the unsolicited region 88 can be encoded using themost robust PHY mode of the system. The unsolicited region 88 can belocated at the beginning of the uplink subframe 85.

The downlink subframe 83 transmits the control data 86 along withdownlink data 82 intended for one or more terminals. Downlink datasymbols 81 are used for transmitting data to the terminals. The symbolsmay be grouped by the PHY mode, terminal identification, and user ID.For example, symbols 81 are grouped by PHY mode, DM2. Thus, the symbols81 destined for terminals that are scheduled to receive during DM2 weremodulated using the same PHY mode. Once grouped by PHY modes, each timeblock is transmitted in a pre-defined modulation sequence using ascheduling approach as previously discussed. For example, DM1 is QAM-4,DM2 is QAM-16, DM3 is QAM-64, and DM4 is QAM-256. In any downlinksubframe 83, any one or more of the PHY modes may be absent.

The data transmitted during frame 80 is in the form of symbols 81.Communication systems that operate using the LMDS band map QuadratureAmplitude Modulation (QAM) symbols to each time block of frame 80.Alternatively, communication systems that operate using the MMDS band dothe same or may map Orthogonal Frequency Division Multiplexing (OFDM)symbols to each time block of frame 80.

FIG. 2 also shows an exemplary downlink mapping of a stream of variablelength media access control (MAC) messages 1200 to symbols 81 fortransmission during the frame 80. More specifically, the mapping shownin FIG. 2 is used for messages intended for terminals with the samepreferred PHY mode, DM2. One or more MAC messages 1200 are fragmentedand packed into Transmission Convergence Data Units (TDUs) 1206. EachTDU 1206 includes downlink data 82(b) in the form of i bits which mayinclude Transmission Convergence (TC) layer overhead. Each TDU 1206 fora given PHY mode has a fixed length. For example, in FIG. 2, each TDU iscomprised of i=228 bits which include 20 bits of TC overhead resultingin the ability to carry 208 bits of MAC message data. Forward errorcorrection (FEC) j bits are added to the i bits of the TDU 1206 to formPhysical Information (PI) elements 1202, alternatively called FECblocks. Each PI element 1202 has a length of k bits (i bits+j bits). Theaddition of j bits reduces the likelihood of bit errors occurring duringdemodulation by the terminals. For example, the 228-bit TDUs 1206 can bemapped to 300-bit PIs 1202 by encoding the data in the TDUs 1206. The228-bit TDU 1206 may be encoded using the well-known Reed-Solomon codingtechnique to create the 300-bit PI elements 1202. Other minimumquantities of the physical and logical units can be used withoutdeparting from the scope of the present invention.

Padding may be added to a MAC message to form an integer multiple ofTDUs 1206. For example, FIG. 2 shows padding being added to “message n”so that the result will form an integer multiple of TDUs 1206 and,therefore, an integer multiple of PI elements 1202. The padding can usea fill byte, for example, 0×55. Alternatively, the last PI element 1202may be shortened, if allowed by the FEC, resulting in a shortened TDU.The process of producing shortened PI elements 1202, a.k.a. FEC blocks,is well-known in the arts.

The PI elements 1202 are then modulated using a modulation scheme toform symbols 81. For example, QAM symbols or OFDM symbols could be used.The number of symbols 81 required to transmit the PI elements 1202 mayvary with the PHY mode selected. For example, if QAM-4 is used for DM2,each resulting symbol represents two bits. If QAM-64 is used for DM2,each resulting symbol represents six bits. For convenience, multiplesymbols can be further mapped to a physical slot (PS) to decrease thegranularity of the data allocation boundaries. For example, a 4-symbolphysical slot could be used to decrease the number of bits required toexpress allocation boundaries in maps.

FIG. 3 is a block diagram of functional elements of an exemplarytransmitter 40. The transmitter 40 can include a convolutional encoder42, a block encoder 44, a M-ary Modulator 46, and an up-converter 49.The transmitter 40 receives 1 bits of data and encodes the data, packsthe encoded bits of data into frame 80 and upconverts the frame of datato a transmission frequency. The convolutional encoder 42 and blockcoder 44 supply the FEC data that converts the i bits of data into FECblocks. For example, the convolutional encoder 42 can use a selectedratio to encode i bits of data. The block coder uses the selected codelevel to encode the convoluted data to produce FEC blocks.

Then, the M-ary QAM modulator converts the FEC blocks into QAM symbolsbased on the selected bit per symbol rate for each time block. Thesymbols can then be inserted into the frame 80 using a schedulingtechnique. Up-converter 49 frequency shifts the packed frame of data toa frequency suitable for transmission between a terminal and basestation based on schemes known to those of skill in the art.

FIG. 4 is a block diagram of functional elements of an exemplaryreceiver 50. The receiver 50 converts the frequency shifted frame ofdata back into groups of bits of data. The receiver 50 includes adown-converter 59, M-ary QAM demodulator 56, block decoder 54, andconvolutional decoder 52. The down-converter 59 frequency shifts thereceived signal back to baseband using schemes known to those of skillin the art. Block decoder 54 decodes the symbols into FEC blocks usingschemes known to those of skill in the art. Then, the convolutionaldecoder decodes the FEC blocks to produce i bits of data. The methodsand frame structures described below are performed by the functionalelements of the transmitter and receiver described above with referenceto FIGS. 3 and 4.

Referring now to FIG. 5, a frame structure 90, which has been adaptedfrom frame structure 80 (see FIG. 2), for use in a FDD communicationsystem is shown. The terminals and base station communicate using aseries of uplink subframes and a series of downlink subframes. FIG. 5illustrates two uplink subframes 92(a), 92(b) in a series of uplinksubframes and two downlink subframes 94(a), 94(b) in a series ofdownlink subframes. The downlink subframe is transmitted simultaneouslywith the uplink subframe on different frequency carriers. This is notpossible in the TDD system of FIG. 2. Between the downlink and uplinksubframes, the modulation regions may differ in size. This is generallyuseful, since uplink and downlink data amounts are likely to varybetween different terminals. The different modulation densitiesavailable to different terminals will affect the transport time theyrequire.

In the FDD frame structure 90, the uplink and the downlink operation mayor may not be synchronized. For example, a frame start and a frame end,hence frame length, may be identical, or not, depending on the specificimplementation. The FDD frame structure may apply adaptive modulationonly for the downlink and use a different scheme for the uplink. Forexample, a fixed modulation scheme could be used for the uplink.Conversely, a different scheme (e.g. fixed modulation) can be used onthe downlink, while using adaptive modulation on the uplink.

FIG. 6 shows an arrangement for arranging data from multiple terminalsinto a single Time Division Multiplexing (TDM) time block. Terminalsreceiving the same modulation (or, more generally, having the samemodulation and FEC, i.e. PHY mode) will often be grouped together fordownlink transmissions. The data from all terminals using the same PHYmode are multiplexed together. This means that various data packets 102associated with one terminal could be mixed with data packets of otherterminals depending on the exact queuing mechanism which prepared thedata for transmission. In this case, while a terminal is receiving adownlink transmission it is required to demodulate all symbols in thetime block which uses its assigned modulation. A higher layer addressingmechanism, such as headers, associates the terminal with the databelonging to it.

FIG. 7 shows a potential downlink conflict for an FDD terminalrestricted to half-duplex operation. The half-duplex terminal canrepresent a terminal 30, 32, 34, 36, 38 (see FIG. 1) operating in an FDDcommunication system. The half-duplex terminal is unable tosimultaneously receive while transmitting. The half-duplex terminal hasknowledge of the least robust PHY mode the base station will use totransmit, and will listen to PHY modes which are at least as robust asits preferred PHY mode. However, the half-duplex terminal will be unableto listen to PHY modes that conflict with their scheduled uplink events.Thus, a conflict can occur if the terminal was scheduled to transmit tothe base station while receiving from the base station.

To prevent a conflict from occurring, the terminal's uplink transmission(Tx) event 110 is preferably not scheduled at the same time as itsdownlink event 112. However, the terminal may lose synchronization withthe base station during its uplink Tx event 110 and be unable tore-synchronize prior to the base station transmitting its downlink event112. The loss of synchronization may become more problematic in acommunication system that includes multiple terminals restricted tohalf-duplex operation. For example, in a case where all of the terminalsin an FDD communication system operate in a half-duplex fashion, timegaps may occur in a frame during a downlink or uplink. Such time gapsmay constitute a significant part of that portion of the frame to whichsuch a terminal's use is restricted.

The downlink subframe structure shown in FIG. 7 alleviates this issue byallowing re-synchronization of half-duplex terminals during the downlinksubframe. Specifically, the frame structure of the downlink 94 is TimeDivision Multiple Access (TDMA). The TDMA structure allocates a portionof the downlink subframe for preambles 106. If a terminal losessynchronization with the base station during the uplink Tx event 110,the preamble 106 allows the terminal to re-synchronize with the basestation prior to receiving its downlink.

Each terminal synchronizes and picks up control data 114, includinguplink and downlink mapping information, at the beginning of everydownlink subframe 94. The uplink map defines when the next uplink Txevent 110 will occur for each terminal in the uplink subframe 92.Similarly, the downlink map is used by terminals to determine whendownlink events 112 will occur in the downlink subframe 94. For example,a downlink map entry can indicate when the downlink subframe willtransmit data with a specific PHY mode.

Uplink and downlink events can contain data associated with more thanone user of the terminal. Higher layer addressing may be applied todetermine specific associations of user data. The downlink map entry isnot required to contain terminal identification information. Instead, aterminal which ended its uplink transmission and is available fordownlink reception can use the downlink map to determine the next eventwhich is relevant for it, that is, the next event that uses itspreferred PHY mode, i.e. modulation parameters and FEC, which correspondto its settings. This mapping information will be further explained withreference to FIG. 9. The downlink event 112 for a terminal is precededby a preamble 106 in the downlink subframe 94. The preamble allows theterminal to quickly re-synchronize prior to demodulating the data in thedownlink event 112. When the downlink event 112 ends (meaning thatdemodulation process of the associated data terminates), the terminal isready for the next uplink Tx event as defined in the uplink map.

FIG. 8 is a mapping diagram for a combined FDD TDM/TDMA downlinksubframe for use with half-duplex and full-duplex terminals. When an FDDcommunication system includes differing terminal types, i.e. half-duplexand full-duplex, additional scheduling difficulties may occur. The framestructure shown in FIG. 8 alleviates these issues by combining TDMA andTDM in a single downlink subframe 124. The TDM is utilized for bandwidthefficiency and the TDMA is used for half-duplex terminal support as willbe explained below. In an FDD communication system having onlyfull-duplex terminals, there is no need to use the TDMA portion. Thesame is true for any individual frame in which only full-duplexterminals are scheduled to transmit in the uplink. Conversely, in atypical TDD communication system only the TDM portion needs be used evenif the communication system includes half-duplex terminals. However, theuse of the TDMA portion in a TDD communication system allows the basestation to utilize a smart antenna for downlinks. In such a TDD system,each terminal can re-synchronize with the base station during thedownlink subframe.

Each downlink subframe 124 can include a frame control header 125 anddownlink data 121. The frame control header 125 can include a preamble126, PHY control information 127, and media access control (MAC)information 128. The preamble 126 is used for synchronizing theterminals with the base station. For example, preamble 126 allows theterminals to synchronize with the base station at the beginning of thedownlink subframe 124. The preamble can be transmitted using a robustPHY mode. A robust PHY mode allows terminals that are configured forreceiving only robust modulation schemes to demodulate the preamble andsynchronize with the base station.

The PHY control information 127 can include a downlink map 123. Thedownlink map 123 indicates to the terminals where and what modulationchanges occur in the downlink data 121. An exemplary downlink map 123 isdiscussed below with reference to FIG. 9.

The MAC control information 128 provides terminals with instructions ontransmission protocols for the uplink subframe. These instructions caninclude an uplink map 129. The uplink map 129 is a map of a subsequentuplink subframe that is to be transmitted by the terminals.

To minimize errors in the mapping process, the base station transmitsthe downlink map and the uplink map using a robust PHY mode. Moreover,the base station can allocate a minimum number of symbols for the TDMportion 122 to accommodate the time required for the terminals toprocess and act upon the first downlink map entry. The downlink map 123is the first information broadcast to the terminals in a downlinksubframe to maximize the amount of time between receiving the downlinkmap and when the first terminal is required to act based on the downlinkmap. All other control information 125, including the uplink map 129,can come after the broadcast of the downlink map 123.

A full-duplex terminal, and any half-duplex terminal that receives laterthan it transmits within a frame, can take advantage of the TDM portion122 of the downlink subframe 121. Thus, the downlink data 124 startswith a TDM portion 122. Additionally, to increase statisticalmultiplexing gain, it should be noted that full-duplex terminals arealso able to re-synchronize with the base station in the TDMA portion120 to receive data. Accordingly, the downlink subframe 124 isconstructed with a TDM portion 122 followed by a TDMA portion 120. Thedownlink map 123 for a pure TDMA downlink subframe would have the samenumber of map entries as the TDM/TDMA downlink subframe of FIG. 8.However, differences include the presence or absence of preambles 106 inthe TDMA portion 120, and the desirability of ordering the TDM portion122 by PHY mode robustness.

FIG. 9 shows the structure of an exemplary downlink map 123 from FIG. 8for use with a TDM/TDMA frame structure. The downlink map 123 allows theterminals to recognize PHY mode transitions in the downlink. Theexemplary downlink map 123 can be any sequence of time indicatorspointing out transmission location (such as by referencing start andend, or start and length, or offsets relative to a previoustransmission) and terminal identification associating the map entry witha specific terminal. The time location information can be stated as anumber of symbols referenced to frame start, or as any pre-defined unitof time understandable by the terminal. For example, if there are fourmodulation regions then four map entries are expected. If the mapelements are using modulation symbols as time ticks, then a mapcontaining “0123”, “0234”, “1119”, and “2123” is interpreted as DM1starting on symbol 123, DM2 starting on symbol 234, DM3 starting onsymbol 1119, and DM4 starting at symbol 2123.

The exemplary downlink map 123 of FIG. 9 can include a sequence of 20bit entries. In this example, four bits can contain a Downlink IntervalUsage Code (DIUC) entry 142. The DIUC defines the downlink PHY mode foreach PHY mode in the downlink data 121 (see FIG. 8). The DIUC canindicate the PHY mode (i.e. modulation, FEC) and also whether the PHYmode is preceded by a preamble (TDMA) or not (TDM). For example, if abase station had five downlink PHY modes to select from for its downlinktransmissions, the base station would require ten unique DIUCs toidentify the possible combinations. Thus, the DIUCs could describe thetransition points between PHY modes in the TDM portion 122 as well asfor each PHY mode in the TDMA portion 120. For example, the downlink map123 may include entries for a begin TDM portion, a TDM transition toQ16, a TDM transition to Q64, an end of TDM portion, and an end of TDMAportion. Some formats have flexibility in terms of channel bandwidth andframe length. In these cases, the PS start field 144 may be used torepresent physical slots rather than symbols, giving lower granularityof downlink allocation.

FIG. 10 shows one relationship between frame mapping data and the datait maps for an FDD communication system. The downlink map 123 (see FIG.8) is valid for the frame in which it appears. For example, the downlinkmap in PHY Ctrl n−1 is valid for frame n−1 131. Similarly, the downlinkmap in PHY Ctrl n is valid for frame n 133. The uplink map 129 (see FIG.8) can be valid for the next uplink subframe as shown in FIG. 10. Theuplink subframe in FIG. 10 is shown synchronized with the downlinksubframe. However, the start of the downlink subframe and the start ofthe uplink subframe do not have to be synchronized. In this case, theuplink map 129 in frame n−1 131 can be valid for an uplink subframe thatbegins during frame n−1 131.

FIG. 11 is a mapping diagram for a FDD TDM/TDMA downlink subframe thatvaries FEC types for a given modulation scheme. The downlink subframe130 is the same as described with respect to FIG. 8 except that a TDMportion 132 and a TDMA portion 134 both use a plurality of different FECtypes in combination with different modulation types. For example, QAM-4is used with FEC a in the TDM portion 132. FEC a is the most robust FECand is used for weak channels. Slightly stronger channels may use QAM-4with a somewhat less robust FEC b in the TDM portion. A less forgivingmodulation, such as QAM-64, may be used with different levels of FEC,such as FEC d and FEC e, in the TDM portion 132. The TDMA portion 134may also be defined by modulation type in combination with FEC type. Forexample, QAM-x is used with both FEC d and FEC c in the TDMA portion 134of the downlink subframe 130.

FIG. 12 is a mapping diagram for a TDM/TDMA downlink subframe thatsupports smart antennae. The downlink subframe 150 is the same asdescribed with respect to FIG. 8 except that the TDMA portion is usedfor all of the downlink data 121. While not recommended for efficiency,a downlink could be scheduled to be entirely TDMA. In practice, the TDMAportion need only be used in the presence of half-duplex terminals in aFDD communication system, and then only when the half-duplex terminalscannot be scheduled to receive earlier in the frame than they transmit.However, by extending the TDMA resynchronization capability to theentire downlink data 121 the base station could use smart antenna forits transmissions. This would allow the base station 20 to transmit toan individual terminal or a group of terminals within cell 10. Eachindividual terminal or group of terminals would be able tore-synchronize with the base station 20 at the beginning of their burst.

Full-duplex terminals and half-duplex terminals that receive before theytransmit could both use TDMA. The order of the PHY modes within thedownlink subframe 150 could be varied. Each terminal would still receivea broadcast preamble 126 from the base station which would indicate whentheir preamble 106 would be transmitted by the base station. The use ofa smart antenna would increase the gain of the received signal at theterminal. However, some bandwidth would be lost due to the addition ofpreambles and map entries.

A TDD communication system could also use the design of the TDMAdownlink subframe 150 to incorporate a base station smart antenna. Inthe TDD communication system, only one channel is used for uplinks anddownlinks. The terminals do not lose synchronization between thebroadcast preamble 126 and the transmission of their data. Thus, if thePHY modes are ordered in the downlink and broadcast to an entire cellwithout a smart antenna, the terminals are able to maintain theirsynchronization. By incorporating a smart antenna at the base station,the terminals within the cell will lose synchronization. However, theuse of a TDMA downlink subframe 150 and its preambles 106 as describedabove would allow the terminals to resynchronize with the base stationprior to receiving their data.

When building an FDD communication system, full-duplex terminals aremore efficiently served by a TDM downlink. Half-duplex terminals,however, are better served by a TDMA downlink. However, in communicationsystems where both full and half-duplex terminals exist, scheduling thedownlink and uplink transmission opportunities for the half-duplexterminals is non-trivial, since these terminals cannot transmit andreceive simultaneously. Some half-duplex terminals may be scheduled toreceive before they transmit. In this case, the base station cantransmit downlink data to such half-duplex terminals in the TDM portion,since these terminals get synchronization from the preamble at thebeginning of the downlink subframe. However, some half-duplex terminalsare unable to be scheduled to transmit after they receive their data.Such terminals would lose the synchronization as they transmit, becausethey complete the transmission in the middle of the downlink subframeand hence have no preamble to use to synchronize their receiver to thebase station.

One solution is to schedule the downlink data transmissions of thesehalf-duplex terminals in a TDMA portion. This allows the terminals toreceive the preamble at the beginning of the TDMA burst for receiversynchronization. Although this approach resolves the problem ofhalf-duplex terminal receiver synchronization, each burst in the TDMAportion requires a DIUC message. The number of DIUC or map entries maygrow if the number of TDMA bursts increases, wasting bandwidth foractual data transmission. Furthermore uplink maps are typically builtonly one frame ahead of time. Therefore, it is not possible to know thesize of the downlink data for those half-duplex terminals in order toproperly schedule the downlink data reception before transmission.

Scheduling Algorithm

A scheduling algorithm will now be described to allow TDM and TDMAportions of a downlink to co-exist in the same downlink subframe. Thealgorithm allows maximum flexibility and efficiency for FDDcommunication systems that must simultaneously support full andhalf-duplex terminals. The algorithm further allows the TDM of multipleterminals in a TDMA burst to minimize the number of map entries in adownlink map. The algorithm limits the number of downlink map entries to(2×n)+1, where n is the number of PHY modes. The algorithm works forpure TDMA downlinks (see FIG. 12), and for downlinks where TDM and TDMAco-exist (see FIGS. 8 and 11). The scheduling algorithm is intended tobe used in communication systems which allocate the uplink subframeahead of building the downlink subframe.

Algorithm Description

First, all terminals are grouped together by the modulation/FEC (PHYmode) in which they receive downlink data. The number of groups formedwill be equal to the number of PHY modes being used for downlink in thecommunication system. Uplink bandwidth is allocated to the terminalssuch that the uplink transmission opportunities of terminals belongingto the same group are kept contiguous in time.

Within these groupings, the uplink bandwidth allocated to an individualterminal is contiguous in time. The groups themselves can be ordered ina particular order to maximize the TDM portion of the downlink. To avoidthe problem of scheduling the downlink and uplink transmissionsimultaneously in time for the terminals within the same group, thedownlink data of the first group is scheduled first to overlap with theuplink bandwidth of the next group to be allocated. This proceeds untilall the downlink data has been allocated.

Notations used in the Scheduling Algorithm

n: the number of downlink (DL) PHY modes (e.g. FEC-type/Modulationcombinations) used by system.

S_(n): set of DL PHY modes, where PHY mode j, is more robust (comesearlier in the downlink TDM section) than DL PHY mode j+1, jεS_(n).

U_(j): total amount of uplink bandwidth, in symbols (or in time, in anasymmetric FDD system), allocated for all terminals that receivedownlink data using DL PHY mode j, where jεS_(n).

D_(j): total amount of downlink bandwidth, in symbols (or in time, in anasymmetric FDD system), allocated for all terminals that receivedownlink data using DL PHY mode j, where jεS_(n).

T: total amount of bandwidth, in symbols (or in time, in an asymmetricFDD system), available on the downlink channel.

u_(k): total amount of uplink bandwidth, in symbols (or in time, in anasymmetric FDD system), allocated for an individual terminal, k.

d_(k): total amount of downlink bandwidth, in symbols (or in time, in anasymmetric FDD system), allocated for an individual terminal, k.

System Constraints

The worst case scheduling is the case where all terminals arehalf-duplex.

For a half duplex terminal k, d_(k)+u_(k)≦T.

There can only be one j, such that D_(j)+U_(j)≧T.

Worst case is when

${\sum\limits_{j \in S_{n}}\left( {D_{j} + U_{j}} \right)} = {2T}$(The link is full, both uplink and downlink).

The following description is shown for the case when n=5. Those skilledin the art will understand that the algorithm may readily be extended toany value of n.

FIG. 13 is a flow chart for a scheduling algorithm. The schedulingalgorithm process begins at a start state 1300. Next at a state 1320,all of the terminals are grouped by their downlink PHY modes. Flowproceeds to a state 1340 where uplink bandwidth is allocated for theterminals. The uplink bandwidth transmission opportunities arecontiguous for terminals with the same downlink PHY mode. The totaluplink bandwidth allocated for group j is U_(j), where jεS_(n). Flowmoves to a state 1360 where the groups are ordered in the downlinksubframe. The uplink groups, U_(j), are put in order of the robustnessof their PHY modes, starting with the second most robust downlink (j=2)and continuing in order of decreasing robustness. The terminal groupwith the most robust DL PHY mode, Un, last. This is shown in FIG. 14.

Flow continues to a state 1360 where the terminal group identified asD_(j), j=1, is allocated downlink bandwidth at the start of the downlinksubframe. Next, at a decision state 1380, the process determines whetherD₁≧U₂. If D₁≧U₂ then flow continues to a state 1400 were the schedulingalgorithm allocates downlink bandwidth for D₁ at the start of thedownlink subframe. This is shown in FIG. 15.

Flow continues to a decision block 1420 to determine whether D₁+U₁≧T. IfD₁+U₁≧T, the process continues to a state 1440 where D₁ is arranged suchthat an individual terminal's bandwidth does not overlap on the uplinkand downlink, even while guaranteeing that the downlink map will notexceed 2n+1. In this case there must be more than one terminalrepresented by D₁.

Returning to decision block 1420, if D₁+U₁≧T is not true, then theprocess continues to a state 1460 where the downlink scheduling becomeseasier since U₂ will not be transmitting while receiving. Subsequentallocations of downlink bandwidth are placed adjacent to the priorallocations. For example, D₂ is placed next to D₁ in FIG. 15.

Returning to decision block 1380, if D₁<U₂, then the process moves to astate 1480 where the scheduling algorithm allocates downlink bandwidthfor D₁ at the start of the downlink subframe. This is shown in FIG. 16.

Flow continues to a decision block 1500 where a determination is madewhether D₂<U₃. If D₂<U₃ is not true, flow continues to state 1460 wherethe downlink scheduling becomes easier since U₃ will not be transmittingwhile receiving. Subsequent allocations of downlink bandwidth are placedadjacent to the prior allocations. For example, D₃ is placed next to D₂.

Returning to decision block 1500, if D₂<U₃, flow continues to a state1520 where the scheduling algorithm allocates downlink bandwidth for D₂at the end of the uplink bandwidth that was allocated for U₂. In thiscase, once the half-duplex terminal assigned to U₂ finishes its uplinktransmission, it will begin receiving its downlink transmission duringD₂ from the base station. A gap in the downlink subframe is left betweenD1 and D2. This is shown in FIG. 17. If D₂ had been allocated downlinkbandwidth adjacent to D₁, a terminal assigned to D₂/U₂ would havepossibly had a conflict. Note that in an event that D₂ overlaps with U₂,terminals can be arranged such that no terminal in this group has uplinkand downlink bandwidth overlap.

Next, at decision block 1540, a determination is made whetherD₃>U₄+U₅+U₁. If D₃>U₄+U₅+U₁ is true, the process continues to a statewhere D₃ is broken into multiple pieces. The pieces are then inserted inthe remaining gaps in the downlink subframe. This is shown in FIG. 18.Note that if D₃ overlaps with U₃, terminals assigned to D₃ can bearranged such that no terminal in this group has uplink and downlinkbandwidth overlap. The process continues to a state 1570 where theremaining downlink bandwidth, located between D₂ and D₃, is allocatedfor downlink transmissions by terminals assigned to D₄ and D₅.

Returning to decision block 1540, if a determination is made thatD₃>U₄+U₅+U₁ is not true, flow continues to decision block 1580 where adetermination is made as to whether D₃<U₄. If D₃<U₄ is not true, theprocess returns to state 1460 where the downlink scheduling becomeseasier since U₄ will not be transmitting while receiving.

Returning to decision block 1580, if D₃<U₄, the process moves to a state1600 where D₃ is allocated a portion of the downlink subframe beginningfrom the end of U₃. A gap in the downlink subframe is left between D₂and D₃. This is shown in FIG. 19.

Next at decision block 1620, a determination is made whether D₄<U₅. IfD₄<U₅ is not true, the process returns to state 1460 where thescheduling is easier. D₄ is placed at the end of its assigned uplink U₄,so that D₄ will downlink once it finishes receiving its uplink, U₄.Subsequent allocations of downlink bandwidth are placed adjacent to theprior allocations. For example, D₅ is placed next to D₄.

Returning to decision block 1620, if D₄<U₅, the process continues to astate 1640 where D₄ is placed at the end of U₄. This is shown in FIG.20. Next, at a decision state 1660, the algorithm determines whether thelast downlink segment D₅ is longer in duration than U₁ and all remainingfragments excluding any fragment that is aligned with U₅. If thealgorithm determines downlink segment D₅ is longer in duration than U₁and all remaining fragments excluding any fragment that is in alignedwith U₅ (as shown in FIG. 21), the process continues to a state 1680where bandwidth rearrangement is performed. There will be other downlinkbandwidth allocations that can be moved in line with U₅ to make room forthe remainder of D₅. The final rearrangement of downlink scheduling isshown in FIG. 22.

Returning to decision block 1660, if the last downlink segment D₅ isshorter in duration than U₁ and all remaining fragments excluding anyfragment that is aligned with U₅, then the process moves to a state 1700where D₅ is placed at the end of D₄ and interleaved in the gaps in thedownlink subframe. No subsequent rearrangement is required. Theforegoing algorithm ensures that the number of map entries will notexceed 2n+1. However, after employing the algorithm, under manycircumstances further rearrangement of the downlink will be possible tofurther reduce the number of downlink map elements below 2n.

While the above detailed description has shown, described, and pointedout novel features as applied to various embodiments, it will beunderstood that various omissions, substitutions, and changes in theform and details of the device or process illustrated may be made bythose skilled in the art without departing from the spirit. The scope isindicated by the appended claims rather than by the foregoingdescription. All changes which come within the meaning and range ofequivalency of the claims are to be embraced within their scope.

1. A frequency division duplexing (FDD) wireless communication methodfor use by a base station, a first terminal, and a second terminal,wherein the base station transmits using a downlink subframe on a firstchannel and the first and second terminals transmit using an uplinksubframe on a second channel, wherein the downlink subframe includes abroadcast preamble, a time division multiplex (TDM) portion, and a TimeDivision Multiple Access (TDMA) portion, and wherein the TDMA portionincludes at least one modulation/forward error correction (PHY) modewith an associated preamble, both of which are intended for the secondterminal, the method comprising: transmitting a broadcast preamble froma base station to a first terminal and a second terminal during adownlink subframe on a first channel; synchronizing the first terminaland the second terminal to the base station based on the broadcastpreamble; transmitting modulated data from the second terminal to thebase station during an uplink subframe on a second channel; transmittingmodulated data from the base station to the first terminal during a TDMportion of the downlink subframe on the first channel after the firstterminal is synchronized with the base station; transmitting a preamblefrom the base station during a TDMA portion of the downlink subframe onthe first channel, wherein the preamble is transmitted after the secondterminal has transmitted its modulated data to the base station;re-synchronizing the second terminal with the base station based on thepreamble transmitted by the base station on the first channel;transmitting modulated data from the base station to the second terminalduring the TDMA portion of the downlink subframe on the first channelafter the second terminal is re-synchronized with the base station, andtransmitting a broadcast downlink map during the downlink subframe fromthe base station which indicates when the TDM portion of the downlinksubframe transitions to the TDMA portion of the downlink subframe. 2.The method of claim 1, wherein the broadcast downlink map includes atleast one time indicator and an associated downlink interval usage code(DIUC), wherein the DIUC indicates the TDMA portion.
 3. The method ofclaim 2, further comprising transmitting a broadcast uplink map duringthe downlink subframe by the base station which indicates when thesecond terminal is scheduled to transmit to the base station during theuplink subframe on a second channel.
 4. The method of claim 3, whereinthe broadcast downlink map identifies a beginning of the TDMA portionwithin the downlink subframe and the broadcast uplink map identifieswhen the second terminal is scheduled to transmit during a next uplinksubframe.
 5. The method of claim 3, wherein the downlink subframe andthe uplink subframe have a combined duration of 0.5 milliseconds.
 6. Themethod of claim 3, wherein the downlink subframe and the uplink subframehave a combined duration of 1 milliseconds.
 7. The method of claim 3,wherein the downlink subframe and the uplink subframe have a combinedduration of 2 milliseconds.
 8. The method of claim 3, wherein theduration of the downlink subframe on the first channel and the durationof the uplink subframe on the second channel vary over time.
 9. Themethod of claim 3, further comprising transmitting modulated data fromthe first terminal to the base station during the uplink subframe on thesecond channel.
 10. The method of claim 9, wherein transmitting by thesecond terminal and transmitting by the first terminal are performedusing different PHY modes.
 11. The method of claim 9, whereintransmitting to the first terminal and transmitting to the secondterminal, both by the base station, is performed using different PHYmodes.
 12. The method of claim 9, wherein transmissions during theuplink subframe and the downlink subframe are modulated using QuadratureAmplitude Modulation (QAM) symbols of adaptable modulation density. 13.The method of claim 9, wherein transmissions during the uplink subframeand the downlink subframe comprise Orthogonal Frequency DivisionMultiplexing (OFDM) symbols of adaptable modulation density.
 14. Themethod of claim 10, wherein the first terminal and the second terminaluse the same modulation type with different forward error correctiontypes.
 15. A frequency division duplexing (FDD) wireless communicationmethod for use by a base station, a first terminal, and a secondterminal, wherein the base station transmits using a downlink subframeon a first channel and the first and second terminals transmit using anuplink subframe on a second channel, whrerein the downlink subframeincludes a broadcast preamble, a time division multiplex (TDM) portion,and a Time Division Multiple Access (TDMA) portion, and wherein the TDMAportion includes at least one modulation/forward error correction (PHY)mode with an associated preamble, both of which are intended for thesecond terminal, the method comprising: transmitting a broadcastpreamble from a base station to a first terminal and a second terminalduring a downlink subframe on a first channel; sychronizing the firstterminal and the second terminal to the base station based on thebroadcast preamble; transmitting modulated data from the second terminalto the base station during an uplink subframe on a second channel;transmitting modulated data from the base station to the first terminalduring a TDM portion of the downlink subframe on the first channel afterthe first terminal is synchronized with the base station; transmitting apreamble from the base station during a TDMA portion of the downlinksubframe on the first channel, wherein the preamble is transmitted afterthe second terminal has transmitted its modulated data to the basestation; re-synchronizing the second terminal with the base stationbased on the preamble transmitted by the base station on the firstchannel, further comprising transmitting modulated data from the basestation to the second terminal during the TDMA portion of the downlinksubframe on the first channel after the second terminal isre-sychronized with the base station; and wherein the first terminaloperates in a full-duplex fashion and the second terminal operated in ahalf-duplex fashion.
 16. A frequency division duplexing (FDD) wirelesscommunication method for use by a base station, a first terminal, and asecond terminal, wherein the base station transmit using a downlinksubframe on a first channel and the first and second terminals transmitusing an uplink subframe on a second channel, wherein the downlinksubframe includes a broadcast preamble, a time division multiplex (TDM)portion, and a Time Division Multiple Access (TDMA) portion, and whereinthe TDMA portion includes at least one modulation/forward errorcorrection (PHY) mode with an associated preamble, both of which areintended for the second terminal, the method comprising: transmitting abroadcast preamble from a base station to a first terminal and a secondterminal during a downlink subframe on a first channel; synchronizingthe first terminal and the second terminal to the base station based onthe broadcast preamble; transmitting modulated data fron the secondterminal to the base station during an uplink subframe on a secondchannel; transmitting modulated data from the base station to the firstterminal during a TDM portion of the downlink subframe on the firstchannel after the first terminal is synchronized with the base station;transmitting a preamble from the base station during a TDMA portion ofthe downlink subframe on the first channel, wherein the preamble istransmitted after the second terminal has transmitted its modulated datato the base station; re-synchronizing the second terminal with the basestation based on the preamble transmitted by the base station on thefirst channel; transmitting modulated data from the base station to thesecond terminal during the TDMA portion of the downlink subframe on thefirst channel after the second terminal is re-synchronized with the basestation; and wherein the first and second terminals operate in ahalf-duplex fashion.
 17. The method of claim 16, further comprisingtransmitting modulated data by the first terminal on a second channelduring an uplink subframe after the first terminal receives modulateddata during the downlink subframe.
 18. The method of claim 16, furthercomprising transmitting modulated data by the second terminal on asecond channel during an uplink subframe before the second terminalreceives modulated data during the downlink subframe.
 19. A frequencydivision duplexing (FDD) wireless communication method for use by a basestation, a first terminal, and a second terminal, wherein the basestation transmits using a downlink subframe on a first channel and thefirst and second terminals transmit using an uplink subframe on a secondchannel, wherein the downlink subframe includes a broadcast preamble, atime division multiplex (TDM) portion, and a Time Division MultipleAccess (TDMA) portion, and wherein the TDMA portion includes at leastone modulation/forward error correction (PHY) mode with an associatedpreamble, both of which are intended for the second terminal, the methodcomprising: transmitting a broadcast preamble for a base station to afirst terminal and a second terminal during a downlink subframe on afirst channel; sunchronizing the first terminal and the second terminalto the base station based on the broadcast preamble; transmittingmodulated data from the second terminal to the base station during auplink subframe on a second channel; transmitting modulated data fromthe base station to the first terminal during a TDM portion of thedownlink subframe on the first channel after the first terminal issynchronized with the base station; transmitting a preamble from thebase station during a TDMA portion of the downlink subframe on the firstchannel, wherein the preamble is transmitted after the second terminalhas transmitted its modulated data to the base station; re-synchronizingthe second terminal with the base station based on the preambletransmitted by the base station on the first channel; transmittingmodulated data from the base station to the second terminal during theTDMA portion of the downlink subframe on the first channel after thesecond terminal is re-synchronized with the base station; and whereinthe first and second terminals operate in a full-duplex fashion.
 20. Themethod of claim 19, further comprising transmitting the TDMA portionduring the downlink subframe from the base station using a smartantenna.
 21. A time division duplexing (TDD) wireless communicationmethod for use by a base station and a first terminal and a secondterminal, wherein the base station transmits using a downlink subframeand the terminals transmit using an uplink subframe, both on the samechannel, wherein the downlink subframe includes a broadcast preamble anda Time Division Multiple Access (TDMA) portion, and wherein the TDMAportion includes a first modulation/forward error correction (PHY) modewith an associated preamble which is only intended for the firstterminal, and a second PHY mode with an associated preamble which isonly intended for the second terminal, the method comprising:transmitting a broadcast preamble from a base station to a firstterminal and a second terminal during a downlink subframe; synchronizingthe first and the second terminals to the base station based on thebroadcast preamble; transmitting a first preamble by the base stationusing a smart antenna to only the first terminal after transmitting thebroadcast preamble, wherein the first preamble is associated with afirst PHY mode; re-synchronizing the first terminal with the basestation based on the first preamble transmitted by the base station;transmitting modulated data from the base station using the smartantenna to only the first terminal during the downlink subframe usingthe first PHY mode after the first terminal is synchronized with thebase station; and transmitting a second preamble from the base stationusing the smart antenna to only the second terminal after transmittingthe modulated data to the first terminal, wherein the second preamble isassociated with a second PHY mode; re-synchronizing the second terminalwith the base station based on the second preamble transmitted by thebase station; transmitting modulated data from the base station to onlythe second terminal during the downlink subframe using the second PHYmode after the second terminal is synchronized with the base station;and transmitting a broadcast downlink map by the base station and duringthe downlink subframe which indicates when the first preamble is to betransmitted by the base station, wherein the broadcast downlink mapincludes at least one time indicator and a downlink interval usage code(DIUC), wherein the DIUC is indicative of the first PHY mode.
 22. Themethod of claim 21, further comprising transmitting a broadcast uplinkmap by the base station and during the downlink subframe which indicateswhen the first terminal is to transmit modulated data to the basestation during an uplink subframe.
 23. The method of claim 22, whereinthe downlink subframe and the uplink subframe have a combined durationof 0.5 milliseconds.
 24. The method of claim 22, wherein the downlinksubframe and the uplink subframe have a combined duration of 1milliseconds.
 25. The method of claim 22, wherein the downlink subframeand the uplink subframe have a combined duration of 2 milliseconds. 26.The method of claim 22, wherein the duration of the downlink subframeand the duration of the uplink subframe vary over time.
 27. The methodof claim 22, wherein transmitting to the first terminal and transmittingto the second terminal, both by the base station, is performed usingdifferent PHY modes.
 28. The method of claim of 27, whereintransmissions during the uplink subframe and the downlink subframe aremodulated using Quadrature Amplitude Modulation (QAM) symbols ofadaptable modulation density.
 29. The method of claim 27, whereintransmissions during the uplink subframe and the downlink subframecomprise Orthogonal Frequency Division Multiplexing (OFDM) symbols ofadaptable modulation density.
 30. The method of claim 27, wherein thefirst terminal and the second terminal use the same modulation type withdifferent forward error correction types.
 31. A frequency divisionduplexing (FDD) wireless communication method for use by a base stationand a first terminal and a second terminal, wherein the base stationtransmits using a downlink subframe on a first channel and the terminalstransmit using an uplink subframe on a second channel, wherein thedownlink subframe includes a broadcast preamble and a Time DivisionMultiple Access (TDMA) portion, and wherein the TDMA portion includes afirst modulation/forward error correction (PHY) mode with an associatedpreamble which is only intended for the first terminal, and a second PHYmode with an associated preamble which is only intended for the secondterminal, the method comprising: transmitting a broadcast preamble froma base station to a first terminal and a second terminal during adownlink subframe on a first channel; synchronizing the first and thesecond terminals to the base station based on the broadcast preamble;transmitting a first preamble by the base station using a smart antennaon the first channel to only the first terminal after transmitting thebroadcast preamble, wherein the first preamble is associated with afirst PHY mode; re-synchronizing the first terminal with the basestation based on the first preamble transmitted by the base station;transmitting modulated data from the base station using the smartantenna on the first channel to only the first terminal during thedownlink subframe using the first PHY mode after the first terminal issynchronized with the base station; transmitting a second preamble bythe base station using the smart antenna on the first channel to onlythe second terminal after transmitting the modulated data to the firstterminal, wherein the second preamble is associated with a second PHYmode; re-synchronizing the second terminal with the base station basedon the second preamble transmitted by the base station; transmittingmodulated data from the base station on the first channel to only thesecond terminal during the downlink subframe using the second PHY modeafter the second terminal is synchronized with the base station; andtransmitting a broadcast downlink map by the base station and during thedownlink subframe which indicated when the first preamble is to betransmitted by the base station, wherein the broadcast downlink mapincludes at least one time indicator and a downlink interval usage code(DIUC), wherein the DIUC is indicative of the first PHY mode.
 32. Themethod of claim 31, further comprising transmitting a broadcast uplinkmap by the base station and during the downlink subframe which indicateswhen the first terminal is to transmit modulated data on a secondchannel to the base station during an uplink subframe.
 33. The method ofclaim 32, wherein the downlink subframe and the uplink subframe have acombined duration of 0.5 milliseconds.
 34. The method of claim 33,wherein the downlink subframe and the uplink subframe have a combinedduration of 1 milliseconds.
 35. The method of claim 33, wherein thedownlink subframe and the uplink subframe have a combined duration of 2milliseconds.
 36. The method of claim 33, wherein the duration of thedownlink subframe and the duration of the uplink subframe vary overtime.
 37. The method of claim 33, wherein transmitting to the firstterminal and transmitting to the second terminal, both by the basestation, is performed using different PHY modes.
 38. The method of claimof 37, wherein transmissions during the uplink subframe and the downlinksubframe are modulated using Quadrature Amplitude Modulation (QAM)symbols of adaptable modulation density.
 39. The method of claim 37,wherein transmissions during the uplink subframe and the downlinksubframe comprise Orthogonal Frequency Division Multiplexing (OFDM)symbols of adaptable modulation density.
 40. The method of claim 37,wherein the first terminal and the second terminal use the samemodulation type with different forward error correction types.